Divers work in dangerous environments that place severe constraints on the types of activities that divers can accomplish. The development of a underwater robotic assistant may help a human diver accomplish tasks more efficiently and safer. However, before Underwater Human-Robot Interaction (UHRI) can be deployed in the field, the UHRI algorithms must be tested and validated in a simulator. In order to test future UHRI algorithms and behaviors, an underwater simulator, based on the Modular OpenRobots Simulation Engine (MORSE) was developed. The Mission Oriented Operating Suite (MOOS) autonomy framework was integrated with the Robot Operating System (ROS) and MORSE to demonstrate a basic UHRI scenario: the VideoRay Pro 4 Remotely Operated Vehicle (ROV) trailing a human diver. The UHRI simulator makes use of other open source projects to enable the programmer to easily incorporate new 3D models into MORSE and adjust the fidelity of sensor and motion models based on scenario goals.